One of the easiest places to find heroin in Paris is in the streets in and around the Gare du Nord, a stone's throw away from the Eurostar terminal. I know about this place partly because I live in Paris and I am a frequent Eurostar traveller, and partly because this is where Google sent me when I typed in the request "Where to find heroin in Paris". Apparently the most popular spot for dealing is the rue Ambroise-Paré which contains a series of entrances to underground car parks where users can shoot up in relative privacy. The place permanently stinks of piss and is under constant police surveillance, as dealers and clients scurry back and forth between their hiding places. You can watch all of this action, nibbling on a snack and sipping champagne, from the front end of the Eurostar VIP Lounge which backs on to the street.

In fact although there are plenty of drugs around the Gare du Nord there is not much real heroin. Most popular with the young homeless population is a substitute called skenan, capsules of morphine sulphate. Aside from skenan, or alongside it, these young people, and older raddled boozers, drink Viking-strength lagers which smell even from a distance like pure ethanol. According to real heroin lovers, in contrast, the best drugs supermarket in this part of town is half a mile away down in Chateau Rouge and Strasbourg Saint-Denis. Actually, I am told that you could probably find heroin in most parts of the city if you look hard enough, but this particular area has a long tradition of busy criminality and a reputation for being relatively police-free.

I should say from the outset I am not a heroin user and I only really began to find out about the Parisian drug scene a few months ago when, with my friend and producer Geoff Bird, I started to write a documentary for Radio 4 called Heroin. In this programme we wanted to investigate the contribution, positive or negative, that heroin had made to 20th-century culture. Our starting point was that the beneficial effects of hallucinogenics (mainly pot and acid) on our culture are now a widely acknowledged fact. Despite their dangers – which are many – no one could deny that the works of Bob Dylan, the Beatles or Syd Barrett, and countless others, have been enhanced by the electric glow of the psychedelic experience. No one, however has ever seriously argued that heroin too can unlock creativity, albeit in a very different way.

We went to Berlin and Paris, mainly because heroin has been a crucial part of their identity. At no point did we wish to glamorise or promote the drug; it was a given that in these cities countless lives had been wrecked by heroin. In the first instance, though, we spoke to heroin users who were unashamed about their habit. Some of them even said that heroin made them better people. This lack of secrecy and guilt is most visible on the internet, where there is now a proliferation of blogs and websites where, like any other consumers, heroin users compare prices, quality, the "taste" and purity of the product. The knock-on effect of this is that, wherever you live, it is easy these days to launch a quick Google search, as I did in Paris, and find a variety of locations and prices, pretty much as if you were looking for a niche restaurant or a specialist club.

These days in the cheerfully "out" international heroin community, users contact each other and talk about heroin rather as if it were a fine wine. In New York City, some heroin lovers have gone as far as collecting the tiny bags in which the drug is sold. The speciality of New York and Brooklyn is that these bags are often stapled with a sharp, satirical imprint from the dealer – "Starbucks" is popular, as are "Lazyboy", "Happy Hours", "No Exit" and "Osama bin Laden". In recent years, collections of these bags have been exhibited at galleries in the Lower East Side, just as if they were entirely legitimate works of art. Actually, in many ways, that's what they are – the true artistic ephemera of the streets of New York.

Most people in Britain have never seen, let alone knowingly used "heroin' – which is simply the street name of diamorphine, the most powerful painkiller known to man and still widely used by doctors. Although diamorphine was invented in Britain in the 1870s, by two chemists working in Manchester and London, it was first patented in the 1900s in Germany by the Bayer Company of Elberfeld, which promoted it as a non-addictive cough suppressant and called this new medicine heroin from the German heroisch (heroic) – the first users claimed that this was how it made them feel.

According to the blogs, the quality of heroin in the UK these days is not that good – it is generally estimated to be between 10-20% of purity as compared with US-quality of up to 60%. The main two types are white, the strongest form, from Asia, and brown. It's much easier to find brown – a rougher lower-grade from Afghanistan, which according to one user looks like "deep-fried Coca-Cola". Heroin is, however, still basically a form of morphine – the "heroin" effect is created by the way in which the drug accelerates the release of morphine into the brain.

Anybody who has ever suffered extreme pain, from a heart attack to cancer, will have encountered this drug and been grateful for the way it kills their pain. For all the powerful taboos around the drug, it's also worth pointing out that if they die in hospital, most people reading this article will end their lives – just like the street junkies of Paris – on heroin.

Christiane Felscherinow today. Photograph: Arne Dedert/Corbis

Christiane Felscherinow is seated very comfortably in a plush sofa in the office of her publishers. We are on the second floor of a slightly rundown apartment building in the Charlottenberg district of Berlin; Christiane is a handsome woman of 51, with startlingly clear eyes and a ready smile. She is also the most famous heroin addict in Germany, if not Europe, and is rumoured to be still on the stuff. When I ask her if this is true she becomes giggly, girlish and evasive. "How can I say anything bad about heroin?" she says, not quite answering the question. "Heroin has made me rich. It has made me famous. The other week I travelled on David Bowie's private plane. All of this because of heroin!"

It's hard to tell how much irony is at work here; my bad German and her approximate English don't always quite meet in the middle. An interpreter, Sonia Vukovic, is on hand to help out but it's still not easy to see what Christiane really means. But then her eyes flash with anger. "I love heroin, and I hate it," she says, "But it has been my life – so what can I say?"

This is true. In 1978, at the age of 16, she appeared in a West Berlin court as a witness. By then she had been a heroin addict and prostitute for three years. Two journalists for Stern magazine, Horst Rieck and Kai Hermann, shocked by her appearance and demeanour, interviewed her for two hours after the trial. The interviews then went on for months and eventually Christiane's story became a book Wir Kinder vom Bahnhof Zoo (The Children of Bahnhof Zoo). This was the harrowing but compelling tale not only of how Christiane became a heroin addict, but of a whole generation of children in West Berlin who were dying in a heroin epidemic. Christiane's tale shocked Germany and went on to become a bestseller across Europe. In 1981, it became a film, Christiane F, featuring David Bowie (one of Felscherinow's idols). I remember going to see the film with my younger sister Dawn at the Odeon in Liverpool. We both came out shell-shocked at the horror story that was Christiane's life.

Now Felscherinow has published a second book, Mein zweites Leben (My Second Life), which tells the story of how life didn't necessarily get better after she got famous – there was prison, hepatitis, broken love affairs. Does she have no regrets?

"No, not at all," she says. "This is my life and who I am. How can I regret who I am? Heroin is part of who I am too, so how can I regret it?" As she says this, she looks both cheeky and fun and I wonder if the misery of her story had been exaggerated a little. "Oh no," she says, eyes still twinkling, "it was very hard. But then West Berlin was very hard then. And you had to have a sense of humour to stay alive. You had to have a hard sense of humour."

It's easy to forget what a weird and seedy place West Berlin was in the 1970s and 1980s. This was a place cut off both from western Europe and the east. You had to travel hundreds of miles across East Germany on an autobahn corridor just to get there. It attracted every kind of draft dodger, druggie and dropout from West Germany. Once they got there hardly anybody ever left. This was partly because the place was flooded with hard drugs, mainly heroin, allegedly made in illegal labs in the east. If you were a young person in West Berlin in the 1970s and 1980s it was very hard not to come into contact with these drugs, or end up like Christiane F.

Mark Reeder left Manchester in 1978 for West Berlin and has been there ever since, working as a musician and record producer. He worked for a while representing Factory Records and Joy Division, and recalls the band's first visits to the city ("they were fascinated by all the bullet-holes," he says). He also has seen the effect that heroin had on the city and its culture. After Factory he worked with the likes of Lydia Lunch, Rowland S Howard and the circle around Nick Cave, who claimed that he came to West Berlin in the 1980s to get off the stuff but found it here cheaper and purer than anywhere else in Europe. "That was the problem," says Reeder, "there was so much good heroin in West Berlin that it was a struggle to stay alive. There were a lot of artistic people, German and Anglos, but everyone was wasted. It was all bands could do to play a gig, get paid and then get destroyed on smack." He goes on to describe the effects of the occasional heroin famine on the culture of the city. Heroin withdrawal normally lasts 72 hours and can be the cruellest kind of torture. "You would see people like zombies, the city would go into shutdown, and the clubs were just full of the living dead waiting for a fix. The music would get angrier and more violent. You can hear the tension in any of the bands around then – just listen to Nick Cave's early stuff with the Birthday Party or the Bad Seeds."

We took a walk together in the Schöneberg district of the city, ending up on Genthiner Strasse. This was where the Sound Discothèque was in the 1970s, one of the few nightclubs then in West Berlin, and where Christiane and her generation first discovered heroin. "What shocked me when I got here from Manchester was first of all the kind of music they had here," says Reeder as we stroll past the place where the Sound once was (now a furniture store). "Back in the UK in the late 70s everyone was popping amphetamines and jumping around to punk. But here people were just sitting cross-legged, listening to Tangerine Dream or Klaus Schulze, sort of drone, dream music. The other was the drugs. I had never seen heroin in Manchester, or knew anyone who took it. It was for the Rolling Stones, not the likes of us. Here in Berlin it was everywhere, and everyone was on it."

In some ways, since the fall of the Wall, West Berlin has changed less than East Berlin, where there at least has been a housing boom. Parts of the city are indeed pretty much intact from the bleak and sleazy past. Leaving the ghost of the Sound, we turn left into what was called the Babystrich – this is the strip outside the Sound where Christiane and her mates sold their bodies for smack. Things round here can't have changed much since then – on a blustery Tuesday morning young east European-looking girls are already flagging down cars.

Reeder's theory, and I believe him, is that West Berlin in the 1970s and 1980s was probably the most fucked-up city in Europe, suffering from the catastrophe of a war that didn't quite seem to be over and the deep psychic trauma of being lost between east and west. Eventually, the likes of Iggy Pop and David Bowie gave Berlin an international visibility as a glamorous and decadent location, but all of this was on the surface. "Everything then was chaos," says Felscherinow, not without a touch of nostalgia. "You could live how you wanted. You could get it when you wanted. That was West Berlin. It was never easy to live here, but that was the point."

This sounded to me like a painful way to live. "Yes you can say that," she says, her eyes now focused on her cigarette. "We lived in pain. We had withdrawals a lot and so we suffered a lot. We were masochists. This was a city in pain."

The Hotel de Lauzun on the Ile Saint-Louis, could not be further removed from the grey streets of Berlin or indeed the grimy streets of the Gare du Nord, less than half an hour's walk away.

The building is set on the north bank of the island, in a dreamy setting where the Seine laps lazily against its banks, and you can barely make out the sounds of the 21st-century city. It is indeed little changed from the 1840s, when the poet Charles Baudelaire lived here. This is where he began composing the book that would become known as Les Fleurs du Mal (The Flowers of Evil) – a compendium of poems on satanism, lesbianism, sex, death and revolt which would eventually be prosecuted on grounds of blasphemy on publication in 1857 (six of the poems remained banned until 1949).

This is also where the Parisian tradition of using opium in the name of artistic inspiration began. With his friend and fellow poet Théophile Gautier, Baudelaire was a founder member of the Club des Hachichins – an elite group of intellectuals and spiritual adventurers (the club also included the painter Eugène Delacroix and the poet Gérard de Nerval). They took drugs in pursuit of what they called "fantasias" – collective and individual experiences of the altered state.

Baudelaire was an avid reader (and translator) of Thomas de Quincey's Confessions of an English Opium Eater of 1821. As such, his sensibility was gripped by opium, which was administered to him as a chewy paste by a certain Dr Moreau, who had travelled in the Orient and was curious about the effect of this narcotic on the cultivated western mind. This was not quite as intense as heroin, but it had a similar impact on the mind and body. Baudelaire described how it could "expand beyond all measures, stretch out the limitless, make rapture bottomless". This is a fairly accurate description of what opium or heroin does when it hits the opioid-receptors in the brain. The drug did not give Baudelaire visions or hallucinations, even if he had wished for them; instead, it threw him into a profound meditation which detached him from the world and made him understand it more clearly.

Chet Baker in the 50s. Photograph: Lebrecht/Corbis

The Parisian tradition of opiate usage reached its zenith in the 1950s when black jazz musicians flocked to Paris, fleeing the racism of the United States, and finding in Paris cheap and good-quality heroin. The heroin in Paris then came from Indochina, via Turkey, and was brought into Marseille by the Corsican gangs who would later be known as the French Connection. The ultimate destination for much of this stuff was the United States, but cosmopolitan Paris too provided a ready market. The drug arrived as morphine paste and was made into heroin in illegal laboratories in Marseille. The first wave of these laboratories was shut down in 1937; but after the second world war it was rumoured that the French and American authorities colluded in keeping the trade alive, partly to allow the gangsters to keep the powerful communists out of the port of Marseille. Either way, the French Connection grew ever more powerful and finally the stuff of myth and movies (the best of which is French Connection II, where Gene Hackman plays a dissolute New York cop at war with the Marseille gangsters).

In Paris, jazz musicians celebrated heroin for the way in which it enabled them to hit the peaks of "transcendent relaxation" in their being and their music – this was the aesthetics of "cool". You can hear this work, for example, in the playing of the young Chet Baker. This was a man who was once so handsome that he was described as the "James Dean of the trumpet". By the time he died in 1988 – he fell to his death from an Amsterdam window, loaded on heroin and cocaine – he had a face like a crumpled sack. Baker came to Paris in the mid-50s and indulged in all the heroin that was on offer. This is when he began to develop his distinctive style – the gentle, spiralling melancholy which is like listening to someone floating in space.

This was the same sensation described by Scottish poet Alexander Trocchi as the "wonderful healing effect" of heroin. Like Baker, Trocchi arrived in Paris in the 1950s – he came from Glasgow with the aim of making a literary career. Then in his early 20s, he was brilliant at everything – writing, editing, talking, seducing women. But above all Trocchi loved heroin. Before long, he declared that he "had decided to make a career out of it".

It was also about this time that Trocchi encountered Guy Debord, who later became famous as the leader of the avant-garde group known as the Situationist International and the author of the massively influential book The Society of the Spectacle. Trocchi fell immediately under his spell. Debord in turn believed in Trocchi as an active "situationist", that is to say someone whose life was a form of serious play. Trocchi himself called shooting up an act of "systematic nihilism" which "threw a purposive spoon into the broth of experience". He describes this in beautifully lucid prose. "Half an hour ago I gave myself a fix," Trocchi wrote, "I stood the needle and the eye dropper in a glass of cold water and lay down on the bunk… The mind under heroin evades perception as it does ordinarily; one is aware only of contents. But that the whole way of posing the question, of dividing the mind from what it's aware of, is fruitless. Nor is it that objects of perception are intrusive in an electric way as they are under mescalin or lysergic acid… It is that the perceiving turns inward, the eyelids droop, the blood is aware of itself."

For the sense of inviolability, some Americans have used the word "cool". For Trocchi, using heroin was the route to creating a new form of human being; he described himself as "a cosmonaut of inner space", exploring unknown frontiers on behalf of the rest of mankind. When, in 1957, Trocchi was arrested in New York on drug charges, Debord and the situationists leapt vigorously to his defence with a pamphlet called "Hands Off Alex Trocchi!" where they described him "as a new type of artist".

Trocchi is, however, only one of a long line of artists who have developed a philosophy of heroin use in Paris. One of the minor literary hits on the Parisian scene in recent months has been a biography of actor-journalist Alain Pacadis, the "punk dandy" who presided over Le Palace, the nightclub that was the Studio 54 of Paris in the 1980s. Pacadis held a doctorate from the Sorbonne and styled himself a "junkie existentialist". He modelled himself on, among others, Robert Malaval, an artist admired and encouraged by Dalí, who described himself as a "suicide of the art world", and who deliberately overdosed on heroin in 1980 while listening to Richard Hell's punk anthem Blank Generation. He died in his luxurious apartment on the rue du Pont-Louis-Philippe, yards away from the Hotel de Lauzun. In his suicide note he wrote that his overdose was his "gift to the future". The French singer Daniel Darc, who died of an overdose in February, spoke about how his heroin addiction placed him in a pantheon of French users, who from Baudelaire to Pacadis, via Artaud, Cocteau and the surrealists, have taken drugs not to expand the mind but to travel deeper into what Georges Bataille called the inner experience – the complete collapse of the ego into the limitless space of the universe, the "rapture bottomless" of Baudelaire.

If heroin in Berlin is a product of history and politics, it seems then that heroin use in Paris has been a more self-consciously intellectual affair. I put this to Will Self, who is sitting in my office in Paris. Self rarely or never discusses heroin these day, and in particular his own 14 years of heroin use. This is partly because he's bored by it, and partly because he is wary of the cultural slumming that goes with the territory. But Self is not just a novelist but also a professor of contemporary thought at Brunel University. As such he is willing to talk ideas for Radio 4.

"I think the relationship between heroin and cities, or cityspace, is very interesting," he says. "It has more to do with spatiality, how the inner world of the user connects with the outside word of reality. And what we're really talking about is the psychogeography of heroin. William Burroughs knew this when he wrote The Naked Lunch, the great heroin novel set in the Interzone of Tangier, and Lou Reed knew this. The first Velvet Underground album is essentially a day in the life of a heroin addict in New York City, and a map of where he goes and what he sees and what he feels. And the music sounds like heroin, with its drones and impatient feedback and stuttering words. It's the perfect soundtrack to the junkie life. There is a heroin psychogeography – where to find it, where to buy it, where you can smell it." He goes on: "The point is that heroin users occupy a certain negative space in the world, in society. Burroughs writes in The Naked Lunch how, strung out in Tangier, he could sit and look at his shoe for eight hours. Heroin users don't need to do anything or go anywhere: they just are."

This above all is what makes the heroin user a threat to a society built on speed and movement. Heroin, in contrast, makes the individual deeply introspective. Beyond the "dirty junkie" cliches and the fear of disease, one of the reasons why heroin is still taboo is that it wipes away the sense of responsibility to the collective, to the herd. This is why heroin users are usually characterised as self-destructive narcissists who don't really deserve to survive their habits.

But it is clear that artists who are heroin users have a clearly developed sense of negativity in relation to society, and that has its own aesthetic. This indeed is the true art of heroin – to refuse life, to refuse society; terrifyingly, in every absolute sense: to just say "no".